This crank bolt won’t come loose whatsoever

if you can’t add more force, increase mechanical advantage by adding length to the tool and the crank.
some people try a 2×4 softwood board between the crank and the frame to block it from rotating so they don’t have to hold it down. there’s also a tool made for that. but if you can use a cheater pipe on the crank arm and the tool, you can use your body weight. keep your face clear in case a tool slips.